Certain Position-measuring devices are described in a number of documents. They are used for measuring lengths or angles in machines and devices. Such position-measuring devices include a measuring standard, on which one or more code tracks are applied, and a scanning unit, which scans the code tracks and converts path changes and angular changes into electrical signals. In the case of an angle-measuring device, the measuring standard may be a code disk, on which the code tracks are concentrically positioned. In the case of linear measuring devices, the measuring standard may take the form of a ruler.
In addition, certain conventional position-measuring devices, e.g., angle-measuring devices, include, in addition to the code disk for measuring the rotational angle of a shaft, further code disks, with the aid of which the number of completed revolutions is measured.
These additional code disks are driven via a reduction gear that reduces the speed of the shaft in a suitable manner. Such angle-measuring devices are also referred to as multiturn rotary transducers.
Certain linear measuring devices include rulers that are subdivided into several consecutive position segments, in which the coding of the code tracks cyclically repeats in the measuring direction. In order to count the passed position segments, one or more code disks are provided which are driven via a reduction gear during the scanning of the ruler, in a manner analogous to the multiturn rotary transducer.
In order to be able to fulfill the requirements for an arrangement of a multiturn rotary transducer that is as simple and compact as possible, the scanning regions of the code tracks of the different measuring standards should be concentrated in a small space. This allows several, or even all, of the code tracks to be scanned at one location, using, in an ideal example, only one sensor component, a so-called opto-ASIC.
Japanese Published Patent Application Nos. 11-132792 and 63-237616 describe multiturn rotary transducers having a code disk for ascertaining the angular position of a shaft, as well as a further code disk for counting the completed revolutions of the shaft. The two code disks are connected via a reduction gear, and their code tracks are only scanned at one location. A disadvantage of these arrangements is that only one code disk is provided for counting the revolutions, which means that the number of countable revolutions is limited.
European Published Patent Application No. 1 457 762 describes a device for measuring the position, the displacement, or the rotational angle of an object. It includes three measuring standards in the form of three consecutive code disks, which are coupled via a differential gear unit. The code disks are scanned by a scanning unit that radially covers the code tracks of all of the code disks. A disadvantage of a device of this type is that the radiation of the illumination unit must penetrate all of the code disks to scan the outermost code track. The result of this is a high sensitivity to soiling.